In the prior art, in order to proceed with a seismic test in geological prospecting it is necessary to drill a shaft to a certain depth and place a certain amount of explosive within the shaft. Also, in the construction of a highrise building or wharf in a harbor, or in erecting heavy chemical equipment, it is necessary to hammer load bearing piles into the earth to provide a foundation. In such engineering work, apparatus such as an earth boring auger, a vibratory pile driving machine, pile hammer, pulsating drilling machine and/or a spiral piling machine, may be required. These apparatus can either bore a "shaft" of a predetermined diameter or drive a pile column of some length to a predetermined depth. For example, a spiral pile may be sunk to a depth of over twenty meters.
The spiral pile is a steel pipe pile with a spiral fin or blade at its lower end along the outer surface (FIG. 1), requiring a special machine which comprises a moving portion and a fixed portion to move it into the earth. Two or more electric motors are fitted on the fixed portion. The motors operate through a speed variator system to rotate the moving portion which, in turn, is connected to the top of a spiral pile cylinder. The pile follows rotation of the moving portion as it is screwed down into a depth of earth.
Spiral piles of large cross-sectional area including a steel pipe pile having an outside diameter of 35-40 cm and a spiral fin or blade having an outside diameter which ranges from 1-2.5 m, possibly to 3 m, have been constructed. The permissible bearing load of such piles may reach 500 ton or more depending on soil conditions. A large dimension spiral pile may be rotated at a speed of about 0.5-1 revolution per minute; while a smaller dimension spiral pile may be rotated at a speed of up to about 10 revolutions per minute.
Spiral piles have a closed pile head, that is, the lower end of the spiral pile is closed while being sunk. An advantage of having the lower end of the spiral pile closed is that soil is prevented from filling up the pile cylinder. This simplifies the piling process. For example, in screwing down a spiral pile of 30-40 cm diameter to a depth of 10-12 m, an efficiency of 2-3 piles per shift in certain experimental projects has been attained. The spiral pile is applicable to various kinds of soil containing hard clay and bulky entanglements, although it is not applicable with rock. The process of sinking a spiral pile is usually carried out by a crane including a hoist and pile rotating machine for lifting and inserting the spiral pile. Under many circumstances, a spiral pile is more economical than concrete piles and steel piles driven by a pile hammer. However, it is to be appreciated that powerful machinery is indispensable to carry out the piling operation, and the operation also requires steel pipes to be connected together and rotated with the pile to attain a certain depth. Such machinery is hardly able to carry out a piling process in a substantial horizontal direction.
Therefore, in the prior art, when it is required to lay pipe and cable, or to construct an underground tunnel, or a subway in the horizontal direction, the open excavation or trench method is usually adopted. However, if pipe and cable is to be laid below a building, airfield runway, superhighway, railroad bed, river bed, or in other locations at which it is impossible to excavate from the ground surface, the open excavation or trench method is not applicable. The prior art, therefore, has moved to more effective systems of tunneling for pipe and cable laying. These systems may be characterized as the so-called "shield-driven" and "thrustor-driven" systems, both of which are carried without trenching. Thus it is possible to avoid any wracking of the ground. However, it is sometimes necessary that these systems be carried out by removal of scrap earth from the ground by mechanical means or water jet.
An earthwork machine, capable of laying pipe up to a diameter of about 500 cm without trenching has been developed by the Kiev Water Conservancy Engineering Bureau of the Soviet Union. This earthwork machine has been called a "vibratory bullet". The "vibratory bullet" requires no excavation of soil above the pipe, nor does it require soil to be removed from below the pipe. The shell of the "vibratory bullet" (FIG. 2) is made of steel pipe having two conical caps. An eccentric vibrator is fitted inside the shell. The eccentric vibrator is driven by a 10 kw electric motor for developing a circumferential vibration of 2800 cycles per minute. The eccentric vibrator is comprised of two eccentric discs having a moment of 18 kg.cm. In operation, in boring a horizontal passage, it is first required to drill a 75 mm hole for a traction rope which is passed therethrough and connected to the "vibratory bullet". After the eccentric vibrator is started, the "vibratory bullet" is pulled forward by a hoist or tractor to which the other end of the rope is connected. The actual forward speed of the device, in forming a passage in sandy soil is equal to the tractor speed running in third gear. Operation of the device is described in "The Experience of Mechanization in Water Conservancy Engineering" by N. P. Kutlieshenv, Construction Mechanization No. 3, 1958. It is indicated in the article that the wall of the passage, compacted by the "vibratory bullet", will not slump at the time of the laying pipe. And, the article would appear to imply that vibratory action is applicable in some underground work. However, and as previously indicated, it is required that a horizontal pilot hole of a diameter smaller than the diameter of the passage to be formed be drilled beforehand by conventional methods for passing the traction rope for pulling the "vibratory bullet". This preprocess step may create a technically difficult problem, particularly if the pilot hole is of considerable length. Therefore, the "vibratory bullet" has not yet achieved widespread acceptance.